TESTS  OF  CONCRETE  BEAMS  REINFORCED  WITH 

UNIT  FRAMES 


B Y 


NOLAN  DICKSON  MITCHELL 


c,  • 


V* 


O’ 


\v 


THESIS 


FOR  THE 


DEGREE  OF  BACHELOR  OF  SCIENCE 


ARCHITECTURAL  ENGINEERING 


COLLEGE  OF  ENGINEERING 

UNIVERSITY  OF  ILLINOIS 


1910 


UNIVERSITY  OF  ILLINOIS 


June  1,  1910 190 


THIS  IS  TO  CERTIFY  THAT  THE  THESIS  PREPARED  UNDER  MY  SUPERVISION  BY 

NOLAN  DTCKSON  MITCHELL 

ENTITLED  Tests  of  Concrete  Beams  Reinforced  With.  Unit  Frames 


IS  APPROVED  BY  ME  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR  THE 
degree  np B&chel or  of  Science  in  Architectural  Engineering 


Instructor  in  Charge 


Approved 


HEAD  OF  DEPARTMENT  OF 


TESTS  OF  CONCRETE  BEAMS  REINFORCED  WITH  UNIT  FRAMES 


BY  NOLAN  DICKSON  MITCHELL. 

CONTENTS. 

page. 

INTRODUCTION 

Object  of  Tests  1 

Theory  2 

Notation  3 

Shear  4 

Bond  5 

Diagonal  Tension  7 

TEST  SPECIMENS  AND  TESTING  METHODS . 7 

Materials  7 

Cement  8 

Sand  8 

Stone  11 

Steel  12 

Concrete  14 

Test  Beams,  Making  and  Storage  14 

Minor  Test  Pieces  15 

Testing  Apparatus  15 

Observations  18 

CALCULATION  AND  DIAGRAMS  19 

Calculations  19 

Load-Deflection  Curves  20 

Load-Def orme  tion  Dia  grams  21 

« 

Load  and  Position  of  Neutral  Axis  21 


page 


NOTES  OF  TESTS  £3 

Beams  Reinforced  vi  th  Plain  Rods  23 

Beams  Reinforced  with  Gabriel  Units  £4 

Beams  Reinforced  with  Monolith  Units  26 

Beams  Reinforced  with  American  System  Unit  Frames  28 
Beams  Reinforced  with  Corrbar  Unit  Franees  31 

Beams  Reinforced  with  General  Fireproofing 

Company's  Units  33 

CONCLUSIONS  36 

EXPERIMENTAL  DATA,  TABLE  5 40 

PHOTOGRAPHS  OF  TESTED  BEAMS  41 

CURVES  46 

Load-Deflection,  for  Single  Beams,  46 

Load-Deflections,  Averages  for  Three  Beams  52 

Load-Deformation,  with  Diagrams  Showing  Position 

of  Extensometers  and  Crschs  53 

Deformations  and  Position  of  Neutral  Axis  80 


Digitized  by  the  Internet  Archive 

in  2016 


I 


https://archive.org/details/testsofconcretebOOmitc 


TESTS  OP  CONCRETE  BEAMS  REINFORCED  WITH  UNIT  FRAMES. 


INTRODUCTION. 

This  series  of  tests  is  a part  of  the  work  being  carried 
on  by  the  Engineering  Experiment  Station  of  the  University  of 
Illinois  in  the  course  of  the  investigations  of  reinforced  concrete 
begun  in  1904.  Many  problems  of  stresses  in  reinforced  concrete 
beams  have  been  studied  more  or  less  thoroughly  and  many  are  yet 
to  be  studied.  Owing  to  the  extensive  use  of  patented  systems  of 
reinforcement  it  has  been  thought  that  comparative  tests  of  some 
of  these  systems  would  be  of  benefit  to  users  of  concrete  con- 
struction in  general  and  especially  in  cases  where  web  stresses  of 
the  construction  are  an  important  factor. 

Previous  tests  of  the  Engineering  Experiment  Station 
have  been  made  with  regard  to  flexural  stresses,  and  the  relative 
effect  of  plain  and  deformed  bars  on  flexural  strength;  bond  of 
longitudiual  reinforcing  rods;  the  effect  of  various  percentages 
of  reinforcement  and  the  position  of  the  neutral  axis  for  these 
different  bending  moments;  the  ection  of  beams  with  rods  bent  up 
in  various  ways  and  the  effect  of  vertical  stirrups  on  the  shear- 
ing strength  of  beams.  Msny  other  tests  have  been  made  on  beams 
and  concrete  and  afford  much  general  information  in  regard  to  the 
phenomena  of  reinforced  concrete  under  stress.  The  results  of 
much  of  the  work  of  the  Engineering  Experiment  Station  have  been 
set  forth  in  the  form  of  bulletins  issued  from  time  to  time. 

Object  of  Tests:-  The  object  of  these  tests  has  been,  to  compare 
the  various  systems  of  reinforcing  designed  by  manufactures  of 


2. 


unit  frames  with  the  action  of  plain  rode  as  reinforcement  for 
concrete  beams  subject  to  high  shearing  stresses,  to  determine 
the  principal  web  deformations  under  such  stresses  and  to  obtain 
information  which  might  lead  to  the  analysis  of  stresses  in  beams 
with  reinforcement. 

Some  success  has  attended  in  the  first  two  instances 
but  so  far  nothing  satisfactory  in  the  way  of  an  analysis  of  the 
web  stresses  has  been  accomplished.  A comparison  of  the  thirty 
beams  used  in  the  tests  is  made  in  Table5  showing  comparatively 
the  resisting  moments,  stress  in  steel,  stress  in  concrete, 
resistance  to  shear,  and  stresses  developed  in  the  web  reinforce- 
ment; as  well  as  much  other  information  gathered  from  the  tests. 

Theory.-  Reinforced  concrete  being  a combination  of  materials  of 
wholly  different  characteristics,  with  an  arrangement  making  them 
interdependent  in  the  distribution  of  stresses,  makes  the  problem 
of  stress  analysis  much  more  complex  than  that  of  a homogeneous 
material.  Such  facts  as  the  variable  modulus  of  elasticity  of 
concrete,  the  low/  tensile  strength  of  the  material,  the  partial 
rupture  of  the  concrete  under  allowable  working  stresses  of  the 
beam,  and  the  distribution  of  reinforcing  material,  all  tend  to 
make  a rigid  analysis  extremely  complicated.  In  searching  through 
literature  of  the  subject  no  such  analysis  has  been  found.  In- 
stead of  going  into  a strict  analysis  for  the  stresses,  most 
investigators  seem  to  have  made  assumptions  with  the  view  of 
applying  the  results  directly  to  design.  Some  of  the  formulas  for 
resisting  moment  developed  in  this  manner  give  values  corres- 
ponding fsirly  vrell  with  the  results  of  tests  of  beams  subjected 


* 


II 

3. 

to  flexural  stresses.  Shear  formulas,  however,  are  more  in  doubt 
and  scarcely  anything  satisfactory  seems  to  have  been  accomplished 
in  the  analysis  of  the  stresses  in  the  interior  of  reinforced  con- 
crete beams. 


notation: - 

The  following  notation  will  be  used  in  the  discussions. 

b = 

breadth  of  beam. 

d = 

effective  depth  of  beam,  distance  from  the  compressive 
face  to  the  center  of  geometrical  moment  of  the  rein- 
forcing metal. 

A = 

area  of  cross  section  of  reinforcing  metal. 

As 

- area  of  cross  section  of  reinforcing  metal  of  stirrup 

P * 

A 

, ratio  of  area  reinforcing  metal  to  area  of  con- 
crete . 

o - 

perimeter  of  reinforcing  bar. 

m = 

number  of  reinforcing  bare. 

Es  = 

•Modulus  of  elasticity  of  steel. 

Ec  - 

Modulus  of  elasticity  of  concrete. 

IT  = 

ratio  of  moduli  of  elasticity  = 

f - 

tensile  stress  per  unit  area  of  reinforcing  metal. 

c = 

on 

compressive  stress  of  unit  area  of  most  remote  fiber 
of  concrete. 

i 

a = 

distance  from  centroid  of  compression  of  concrete  to 

II 

center  of  tension  of  the  reinforcing  metal. 

c/'  ' 

- j = ratio  of  d'  to  d. 

=•  depth  from  upper  surface  of  besm  to  neutral  axis 
divided  by  d. 

8 = horizontal  distance  between  stirrups, 
s = horizontal  stress  in  concrete  per  unit  area. 


4. 


v = vertical  shearing  stress  per  unit  area  of  concrete, 
u = bond  stress  per  unit  area  of  reinforcing  bar. 
u'  - bond  stress  per  unit  length  of  reinforcing  bar. 

M = resisting  moment  of  a given  section. 

V = total  vertical  shear  8t  a given  section. 

V*  total  bond  between  longituduisl  reinforcement  and  web 
system  in  a length  a . 

x,yf-  coordinates  of  a point  referred  to  the  neutral  axis 
and  the  plane  of  a cross  section. 

Reference  may  be  made  to  Pig.  1. 

Shear:-  The  distribution  of  shearing  stresses  in  reinforced  con- 
crete beams  is  different  from  that  of  beams  of  homogeneous  mater- 
ial having  a straight  line  stress  deformation  relation.  Tn  the 
latter  case  beams  of  rectangular  section  have  a distribution  known 
as  parabolic,  in  which  the  shearing  stresses,  point  by  point, in  the 
depth  of  the  team  may  be  expressed  as  the  abscissae  of  8 parabola 
whose  principal  axis  is  coincident  with  the  neutral  axis  of  the 
beam  8nd  whose  abscissae  are  expressed  by  the  equation, 


which  is  a maximum  when  y - 0,  a minimum  when  y - — . Hence,  the 

maximum  sheering  stress  obtains  at  the  neutral  axis  end  is  equal 
31/ 

to  , while  the  shearing  stress  at  the  surface  of  the  beam 

is  zero.  The  variable  modulus  of  elasticity  of  the  concrete  must 
be  taken  into  account  if  the  exact  shearing  stresses  are  to  be 
found.  For  the  ordinary  working  stresses  of  concrete  the  values 
found  by  the  above  formula  will  not  be  much  in  error  for  the 
portion  of  the  beam  above  the  neutral  axis.  The  nominal  value 
of  the  mean  shear  developed  in  reinforced  concrete  beams  is 


5. 


a J?  o o'  & 


/v&./.  £>/4(5&ws  a^/teraPA/jr/oA/s,  Srerjj^s  /ja/Z)  //v /r,£/A'fro£>c££> 

CfflCffTS  B&4M5. 

<7,  £?z>as  J&<z//g>s7  o£ x-x,  /V&o'/r’cr/ s4x/ls . 

£>,  £>&/b/'/77&'//0/7S 

c,  S/zejS^/eAt//!?/. 
c/,  A/as7?/bcy/ 

e:/4A>c/?oz'<?'z/  //14?£  y€^/h/o/z:e/?7az7/yS e&  '£$0/70/  V. 


6 . 

usually  obtained  by  the  formula, 

v-JL, 

the  analysis  for  which  may  be  found  in  Prof.  Morjeh's  Der  Eisen- 
betonbau,  1906  edition,  page  121. 

Bond.-  In  Bulletin  £9  of  the  Engineering  Experiement  Station 
Professor  Talbot  shows  that  the  bond  stress  developed  in  beams  re- 
inforced with  plain  rods  is, 

7770 cy 

In  some  cases  failure  of  the  beam  is  caused  by  bond  failure  be- 
tween the  concrete  and  reinforcement  and  in  order  to  svoid  such  the 
reinforcement  introduced  to  assist  in  the  distribution  of  web 
stresses  is  firmly  anchored  to  the  horizontal  reinforcing  rods. 

In  the  case  of  anchored  web  reinforcement  the  bond  stress  develop- 
ed is  not  uniformly  distributed  but  is  localized  by  the  reinforce- 
ment to  some  extent.  The  lav/  governing  this  localization  is  not 
known,  but  supposing  the  stirrups  to  be  anchored  at  distances  a 
from  each  other  then  the  bond  developed  in  a length  a.  will  in  gen- 
eral be  the  same  as  for  a uniformly  distributed  bond.  Since  the 
total  bond  developed  per  unit  length  of  beam  is, 

77706/=  , 

c/' 

V being  the  average  shear  over  the  unit  length  in  question;  it 
follows  that  the  total  bond  for  a length  a is, 

T/  _ 

L/a  — — rr  • 

in  which  V is  the  average  shear  over  length  a and  d«  is  the 
average  value  of  over  the  same  length. 


Diagonal  Tension.-  The  second  most  common  failure  of  concrete 


I 


7 


boons  seems  to  be  by  failure  in  diagonal  tension  and  for  this 
reason  the  quention  of  diagonal  tension  seems  to  be  second  only 
to  that  of  direct  flexural  stress. 

From  the  theory  of  stress  distribution  in  a beam  it  is 
found  that  the  vertical  shearing  stress  at  a point  must  be  equal 
to  the  horizontal  shearing  stress  in  order  to  maintain  equilibrium 
and  from  an  analysis  of  the  total  stresses  it  is  found  that  the 
two  principal  stresses  at  any  point  y are  expressed  by  the  equation 

in  which  b represents  tension  or  compression  according  to  sign 
given  to  s.  Substituting  definite  values  for  s and  v it  is  found 
that  the  stresses  are  of  opposite  sign,  (tension  and  compression). 
Substituting  0 for  s,  the  value  obtaining  at  the  neutral  axis,  it 
is  found  that  the  principal  stresses  are  equal,  and  substituting 
0 for  v the  value  at  the  surface  of  the  beam  the  stresses  have 
values  of  s and  0.  From  the  same  source  of  reasoning  it  is  found 
that  the  principal  stressos  are  inclined  at  90°  to  each  other  and 
that  the  angle  which  the  larger  makes  with  the  horizontal  is  ex- 
pressed by  the  equation, 

& = Z arc  /a a ; 

2 ^ 


> 


showing  that  the  angle  of  inclination  of  the  principal  stress  at 
the  neutral  axis  is  45°. 


TEST  SPEC IMSNS  AND  TESTING  METHODS. 

Materials.-  The  materials  used  in  these  tests  were  as  nearly  of  the 
same  character  as  those  used  in  former  tests  as  could  be  obtained 
in  order  that  they  might  be  more  readily  comparable . The  object 
being  to  make  the  principal  comparison  between  different  methods 
of  reinforcing. 


. 


. 


8. 


Cement.-  The  cement  was  furnished  by  the  Universe!  Portland 
Cement  Co.  of  Chicago  for  these  tests.  It  was  pecked  in  cloth 
hags  and  had  been  stored  in  the  concrete  laboratory  for  about  8 
weeks  before  the  beams  were  made.  Samples  taken  from  four  bags 
and  mixed  showed  the  following  properties',  on  a batch  of  neat 
cement  mortar  mixed  with  22.5 $ of  water  showed  a depression  of 
9 m.  m.  under  the  Vieat  needle.  This  batch  appeared  rather  dry 
and  when  once  broken  did  not  adhere  readily.  Pour  batches  of 
mortar  of  the  following  composition  were  made  and  gave  tests  as 
shown  in  Table  1.  Batch  1 of  neat  Universal  Portland  Cement  with 
22.5 $ of  water, batch  2f*l:3  mortar  of  Ottawa  Standard  sand  and 
Universal  Portland  Cement  with  9 . 3$  of  water,  batch  3,8  1:3 
mortar  of  Attica  sand  screened  through  8 Bo.  5 screen  and  Univer- 
sal Portland  Cement  with  9.3 $ of  water,  batch  4 a 1:3  mortar  like 
batch  3 except  that  9.7 $ of  water  was  used.  All  briquettes  were 
kept  under  a damp  cloth  one  day  end  in  water  until  tested. 

Six  pats  of  neat  cement  mortar  kept  under  a damp  cloth 
1 day  end  in  water  or  air  for  balance  of  time  gave  the  following 
results:  after  3 days  all  pats  sound,  after  six  days  pats  in 
air  loose  from  glass  but  sound,  pats  in  water  sound,  after  7 days 
all  sound,  after  14  days  all  pats  loose  from  glass,  but  showing 
no  cracks. 

Sand.-  The  sand  used  was  from  Attica,  Indiana  snd  con- 
tained very  little  clay.  The  weight  of  one  cubic  foot  poured 
loose  was  102  pounds  and  contained  35$  of  voids  as  shown  in  Table 
4.  The  analysis  of  the  sand  as  given  in  Table  2 does  not  show  an 
ideal  gradation  by  any  means. 

U • - 


1 

. 


. 


9 


TABLE  1. 

TENS I IE  STRENGTH  OF  CEMENT. 

Batch  Composition  Strength  in  lbs . per  so . inch 


1 

Universal  Portland 

7 days 
635 

28  days 

710 

Cement  wit&  22.5%  of 

650 

730 

water . 

630 

750 

590 

770 

650 

840 

620 

575  f 

Averages 

629 

760 

2 

1:3  Mortar  of  Ottawa 

130 

105  ? 

Standard  Sand  am  Universal 

145 

170 

Portland  Cement  with  9.3  % 

180 

165 

of  water. 

130 

160 

110 

196 

1 15 

180 

Ave  rage  s 

135 

176 

3 

1:3  Mortar  of  Attica 

145 

165 

Sand  and  Universal 

150 

190 

Portland  Cement  with 

115 

15 0 

9.3  %o  of  water. 

Averages 

137 

169 

4 

1:3  Mortar  of  Attica 

185 

280 

Sand  and  Universal 

120 

220 

Portland  Cement  with 

155 

240 

9.7  %o  of  water . 

Averages 

153 

247 

? Defective  section. 


" ISr*  & -pj/ 


. 


1 1 


■ 


10 


TABLE  2. 


MECHANICAL  ANALYSIS  OP  SA1 TD . 


Screens 

Per  cent 

• 

Pas ping 

Caught 

on 

0.45" 

0.30" 

.60 

ffj* 

0.30 

0.20 

3.19 

0.20 

No.  5 

7. §7 

No. 5 

” 8 

12.38 

" 8 

” 10 

9.83 

7b  oL 

” 10 

” 16 

24.50 

" 16 

” 20 

4.24 

+ / 7» 

” 20 

” 30 

15.20 

” 30 

” 40 

9.21 

7.  + >9 

" 40 

” 60 

8.16 

ri.o% 

" 60 

” 74 

1.44 

" 74 

”100 

1.70 

”100 

"150 

.56 

17* 

”150 

”200 

.20 

1.  V v 

• 

”200 

-- 

.62 

Held  in 

suspension  in 

water  .40 

11. 


Stone.-  The  stone  was  a crushed  Kankakee  limestone  and 
screened  to  pass  a 1 l/4-inch  screen.  It  weighed  82.5  pounds  per 
cubic  foot  poured  loose  and  had  voids  as  shown  in  Table  4.  The 
mechanical  analysis  of  a half  cubic  foot  is  shown  in  Table  3. 

TABLE  3. 

Mechanical  Analysis  of  Stone. 

Screens 


Passing  Caught  on  Per  Cent. 


1 1/2” 

1" 

.25 

1” 

3/4" 

6.69 

3/4" 

1/2"  ^ U> 

41.54 

1/2" 

3/8"  n .f* 

21.44 

3/8" 

7/32"  11 

21.27 

7/32" 

No.  200 

6.61 

Dust 

2.00 

Table  4.  shows  the  voids  in  the  sand,  stone  and  mixtures 
of  sand  and  stone  used  in  the  beams.  Determinations  of  voids  were 
made  in  the  manner  generally  employed  by  the  Experiment  Station. 
The  weight  of  water  required  to  fill  the  voids  of  one  cubic  foot 
of  the  material  divided  by  the  weight  of  one  cubic  foot  of  water 
was  considered  to  be  the  proportion  of  voids. 


12. 

TABLE  4. 


Voids  in  stone,  sand 

and  mixtures. 

Materials 

Condition  of 

Weight  per 

.Per  cent 

Measurement 

cu.  ft. 

of  voids 

Broken  stone 

Foured  loose 

82.5 

44.5 

it  ii 

Y/ell  shaken 

92.5 

39.4 

Sand 

Poured  loose 

102.0 

35.0 

n 

Shaken 

111.4 

32.0 

IT 

Tamped 

114.6 

29.0 

1:2  Mixture  by 

volume 

Sand  and  Stone 

loose , dry 

107.6 

34.3 

II  IT  It 

loose , damp 

100.4 

36.5 

Steel. 

All  the  steel 

used  in  these 

tests  except  the 

straight  rods  of 

beams  280.1,  280 

.2  and  280.3 

W8S  made  up  in  the 

form  of  unit  frames  by  the  severel  companies  furnishing  them.  A 
part  of  the  steel  was  of  the  mild  quality  and  part  of  high  carbon, 
the  exact  properties  were  not  determined  as  no  test  pieces  were 
furnished.  The  quality  of  steel  is  shown  in  Table  5 

The  fabrication  of  the  frames  is  in  some  cases  somewhat 
complicated  and  is  best  shown  by  the  photograph,  Figure  3 
Three  frames  of  ea6h  kind  are  used  in  order  to  get  a better  gen- 
eral knowledge  of  the  action  ss  well  as  more  general  results. 

Some  of  the  units  used  in  the  285  series  were  broken.  The  nature 
of  the  breaks  and  their  effect  on  the  beams  are  noted  under 
Comments  on  Beams  Reinforced  with  the  General  Fireproofing  Com- 
panies Units,  285  series. 


o',  (Ycy/^f/e/  Zrzsss 
j&.  d?£y<fs's&/  Y/P/s'x . 

c./hfc/V^  'syt  Yh’//* 

&£■/?<?/'&■/ '/yh%/&szxa&/7£r  (T&s.  <S/b/y 
3c/.  £bsvr£crs-  £&?//*& 
rfy , sf/77£’S7Ce7/7j~<yj/<?/77  <Y?// /Y&'/77<S’-S 


SSISI* 


14. 


Concrete.-  The  concrete  was  of  a mixture  of  1:2:4 
by  volume,  95  lh.  of  cement  being  considered  as  a.  cubic  foot,  or 
about  1:2. 1:3. 6 by  weight.  The  compressive  strength  of  6 in. 
cubes  at  the  age  of  90  days  was  about  3500  lb.  per  sq.  in.  Average 
values  from  the  tests  of  three  6 in.  cubes  and  one  plain  test  beam, 
6 x 8 x 40  in.  (36  in.  span),  for  each  batch  of  concrete  made  are 
given  in  Table  -5  along  with  the  data  for  the  beams.  The  con- 
crete for  these  tests  was  of  a richer  mixture  and  hence  stronger 
th8n  the  concrete  used  in  previous  beam  tests  in  this  laboratory. 

Test  Beams,  Making  and  Storage.-  All  test  beams  were 
ma&e  with  dimensions  of  8 x 11  in.  x 6 ft.  6 in.  depth  of  10”  from 
upper  surface  to  the  center  of  the  steel,  except  in  case  of  beams 
reinforced  with  Corrbar  Units  in  which  the  total  depth  had  to  be 
increased  to  12  in.  in  order  that  the  center  of  the  steel  might  be 
placed  10”  below  the  surface  of  the  beam. 

The  beams  were  made  in  wooden  forms  with  paper  placed  on 
the  concrete  floor  of  the  laboratory  to  serve  as  the  bottom.  This 
seems  to  be  an  entirely  satisfactory  method  for  making  such  beams 
as  no  trouble  was  experienced  in  any  case.  Practically  all  of  the 
work  of  making  the  beams  was  done  by  laborers  having  some  exper- 
ience in  concrete  construction,  being  directed  as  to  the  manner  of 
placing  the  steel  by  the  laboratory  Assistant  in  charge  of  the 
work. 

The  mixing  was  done  by  hand,  the  sand  being  in  a damp 
state  8nd  stone  wetted  down  before  measuring.  The  sand  and  cement 
were  mixed  and  spaded  together  before  the  addition  of  the  stone. 
After  the  whole  mass  ha. d been  thoroughly  mixed  it  was  wet  down 


with  the  proper  amount  of  water  to  give  the  mixture  the  desired 
consistency  end  turned  twice  more  before  being  pieced.  About  1 in 
of  concrete  was  thrown  into  the  bottom  of  the  form  and  levelled  to 
receive  the  reinforcement  which  was  then  set  part  way  down  into 
the  soft  concrete  and  the  filling  continued.  Frames  which  had 
chairs  or  supports  to  hold  the  main  rods  the  proper  distance  from 
the  bottom  were  set  in  place  before  filling  began  and  the  concrete 
was  spaded  under  all  rods. 

Forms  were  si lowed  to  remain  in  place  seven  days  before 
removal  and  the  beams  were  not  disturb ed  until  about  60  days  old. 

The  only  treatment  received  during  the  curing  was  an  occasional 
sprinkling  from  a hose.  The  temperature  of  the  room  in  which  the 
beams  were  made  varied  from  58s  to  70°  Fa.hr . and  was  in  general 
quite  favorable  toward  obtaining  a good  concrete. 

Minor  Test  Pieces.-  In  order  to  make  a better  compar- 
ison of  the  concrete  of  different  batches  three  6-inch  cubes  and 
one  plain  concrete  beam  6 x 8 x 40  in.  in  size  were  made  from 
each  batch  except  the  last.  Most  of  the  batches  contained  enough 
concrete  to  make  two  beams  and  some  three.  One  set  of  three  cubes 
end  one  smell  or  control  beam  served  as  means  of  determining  the 
quality  of  concrete  of  the  batch. 

Testing  Apparatus.-  All  the  beams  were  tested  on  a 
200,000  lb.  beam  testing  machine.  Loads  were  applied  at  rollers 
on  plates  which  were  bedded  on  the  upper  surface  by  means  of  3 
inch  strips  of  five  ply  rubber  belting  extending  the  full  width 
of  the  beam.  Rocker  pedestals  were  used  to  support  the  bearris  in 
order  to  eliminate  end  restraint.  Strips  of  belting  of  the  same 
size  as  used  in  the  application  of  loads  were  used  for  the  supports 


16. 


end  gsve  in  ell  esses  satisfactory  bearings  for  the  plates.  In 
each  cese  the  rocker  beering  of  the  supports  v;ere  6 feet  epert. 

Deflections  were  measured  at  the  center  of  the  beams 
by  means  of  en  Ames  dial  actuated  by  a projecting  steel  strip 
secured  to  the  side  of  the  beam  by  meens  of  plaster  of  peris.  The 
line  drawing  Fig.£*  show’s  the  arrangement  of  the  deflectometer  as 
well  es  supports  and  method  of  loading.  Extensometers  were  not 
used  on  the  first  three  beams  tested  but  on  all  other  in  various 
arrangements  as  shown  on  the  beam  diagrams  of  Figs.  17  to  43. 

The  instruments  used  were  a modified  form  of  Johnson  extensometer 
secured  to  the  beams  by  drilling  holes  7/16  in.  in  diameter  and 
about  en  inch  deep,  lining  this  with  four  or  five  thicknesses  of 
paper  end  screwing  the  shenk  of  the  diel  to  a snug  fit.  Points 
for  attaching  wires  were  nails  in  thin  blocks  of  wood  set  in 
plaster.  Very  little  trouble  was  experienced  with  this  method  of 
attaching  points*,  only  in  one  or  two  instances  in  the  last  stages 
of  failure  did  the  blocks  drop  off. 

Before  testing  nee rly  all  beams  were  whitewashed  with 
very  thin  coat  of  plaster  of  paris  in  order  to  make  cracks  more 
plainly  visible.  Very  smell  cracks  could,  in  this  wey,  be  de- 
tected as  the  plaster  seemed  to  be  more  brittle  than  the  con- 
crete and  showed  creeks  es  soon  as  the  rupture  begsn. 

Application  of  Loads.-  Loads  v/ere  applied  in  increments 
of  20C0  lbs.,  generally,  with  a rest  of  sufficient  time  to  meke 
readings  of  dial  between  applications.  The  machine  we s run  on 
slow  speed  and  gave  the  application  at* the  rate  of  shout  300C  lb. 
per  minute.  The  time  required  for  the  application  of  the  in- 


17. 


18. 


crement  load  end  readings  of  dials  was  about  2 l/E  minutes. 

Observations.-  Deflections  were  measured  to  .001  inch 
end  estimated  to  .0001,  the  apparatus  giving, in  nearly  all  cases, 

trustworthy  results.  The  dials  used  for  measuring  extensions  were 

Z fc. 

graduated  to  read  direct  to  .jOOS^  inch  and  by  vernier  to.ooo^mch. 

The  results  of  these  measurements  were  much  better  then  anticipat- 
ed and  seem  in  most  cases  to  be  reliable.  Owing  to  the  short 
gage  lengths  and  the  variable  stresses  throughout  this  length  the 
results  shown  are  of  course  only  an  approximation.  In  making  re- 
ductions of  all  extensometer  readings,  excepting,  of  course,  the 
horizontal  measurements  between  load  points,  only  0.6  of  the  gage 
length  was  considered  effective.  While  this  must  necessarily  be 
an  approximation  several  observations  indicate  this  as  a.  proper 
proportion.  The  extent  of  cracks  noted  after  each  load  application 
were  marked  on  the  beam  by  a number  indicating  the  total  load  on 
the  beam.  These  cracks  were  afterward  mapped  in  the  note  book  and 
the  principal  ones  are  shown  on  the  beam  diagrams  of  Pigs.  17  to  43 


. 


. 


■ 


19. 


CALCULATIONS  AND  DIAGRAMS. 


Calculations.-  In  general  the  calculations  are  based  on 
the  methods  of  Bulletin  29  of  the  Engineering  Experiment  Station. 
The  loads  given  are  the  loads  applied  by  the  machines  and  do  not 
include  the  weight  of  the  beam  and  the  small  I beam  used  to  dis- 
tribute the  load.  The  moments  were  obtained  by  the  formula, 

in  which  P is  the  total  load  applied  by  the  machine  and  W is  the 
weight  of  the  portion  of  the  beam  between  supports,  considered  at 
150  lb.  per  cu.  ft.,  and  1 is  the  length  of  the  beam  between  sup- 
ports. Stresses  in  the  longitudinal  reinforcement  were  found  by 
means  of  the  formula. 


A? 

4/’ o' 

for  which  the  values  of  j were  taken  from  the  curve.  Fig.  4,  based 


on  values  given  for  similar  beams  in  Bulletin  29.  Concrete  stress- 
es were  computed  by  the  formula, 


in  which  q is  considered  as  l/4,  in  order  that  the  results  may  be 
comparable  with  others  found  by  the  department.  The  total  shear 
v isjf/jb  W again  being  the  -weight  of  the  portion  of  the  beam  be- 
tween the  supports.  Unit  shear  was  found  by  the  usual  method  of 
dividing  the  total  shear  by  the  width  of  the  beam  times  the  depth 
from  the  centroid  of  compression  of  the  concrete  to  the  center  of 
the  steel;  . In  the  calculations,  the  total  horizontal 

shearing  stress  of  the  beam  was  considered  as  taken  through  the 
bond  between  the  reinforcing  and  concrete.  Hooks  on  the  rein- 
forcement and  bent  up  rods  were  not  considered  as  different  from 


. 


. 


20. 


1 


straight  rods.  Values  of  bond  per  square  inch  of  surface  js-  given 
for  beams  reinforced  with  plain  rods,  in  others  the  values  are  for 
bond  per  linear  inch  of  rod  including  bond  developed  by  the 
stirrups . 

DiagDnal  tension  was  considered  to  be  equal  to  the  unit 
shear  as  tension  in  the  concrete  was  neglected.  The  values 
given  for  stress  in  web  reinforcement  are  higher  than  actually 
occur,  but  it  is  not  known  what  proportion  of  the  stress  is  carried 
through  the  stirrups- so  the  values  given  are  nominal  only  and  may 
be  used  for  comparisons. 

The  modulus  of  rupture  of  the  plain  concrete  beams  was 
calculated  as  for  a material  having  a constant  modulus  of  elas- 
ticity. 

The  photographs  of  the  tested  beams  show  the  failure  cracks 
and  in  most  cases  the  position  of  reinforcement.  In  some  in- 
stances the  failure  cracks  show  larger  than  they  really  were,  due 
to  the  method  of  handling  after  removal  from  the  machine.  This  is 
especially  noticeable  in  beams  280.2,  280.3,  281.2.  On  beams 
281.6,  283.5  and  285.5  parts  of  the  concrete  have  been  knocked 
a way  to  show  the  position  of  the  reinforcement. 

Load-Deflection  Curves.-  The  curves  given  show  the  center 
deflections  of  each  beam.  Total  moments  due  to  loads  and  weight 
of  beam)  are  given  in  parallel  with  loads  on  the  beam  in  units  of 
1000  lb.  in. 

The  load-deflection  curves  given  in  Fig.  16  are  for  the 
average  deflections  of  the  three  beams.  There  are  also  given 
two  load-deflection  curves  of  two  beams  of  the  tests  of  1907. 

These  show  much  greater  deflections,  especially  number  212.6  vj  ion 


21. 


shows  a.  rapid  deflection  from  the  first  application  of  the  load. 

Load-Deformation  Diagrams.-  These  diagrams  are  given  to 
show  the  deformations  of  the  beams  as  measured  in  various  direc- 
tions by  the  extensometers.  In  plotting  these  curves  the  applied 
loads  have  been  laid  off  as  ordinates  and  the  unit  deformation 
as  abscissae.  For  reductions  to  units  deformations  0.6  of  the 
gage  length  has  been  used  as  effective,  except  in  case  of  hori- 
zontal deformations  between  load  points. 

Load  and  Position  of  Deutral  Axis.-  These  diagrams 
show  the  deformations  of  the  concrete  and  steel  to  a scale  of  200 
times  the  unit  deformations.  Values  of  k are  given  in  decimals  of 
the  effective  depth,  d.  These  curves  maybe  of  interest  on  account 
of  the  results  shown  for  high  loads,  in  one  case  50000  lb.  The 
last  curve,  Fig.  48,  does  not  show  very  high  load  values  owing  to 
the  premature  failure  of  the  stirrup  clips  after  which  the  values 
of  k show  to  be  much  larger.  Measurements  for  these  curves  were 
made  on  only  six  beams . 


EUGENE  DIETZGEN  CO.,  CHICAGO. 


. 


, 

■ - ■ 

■ «•  ' . . 

. 

> • - ■'  ' : ' . ■ ' . 


- -r  1 . - , . vr.  fc  i 1 T 


• .......  ; . . ;u  " * . . ! ‘ '•  - I 

I . 1 i , ' 

' 


,,  | 


. 


, 


* 

' 


, ' ' ' ' I I 

.. 

I1 


'h. 


■■  > 


23. 


NOTES  OF  TESTS. 


The  position  of  important  cracks  may  be  seen  on  the  photo 
graphs.  Figs,  b to  y,  also  on  the  diagrams,  Figs.  17  to  43. 

Beams  reinforced  with  plain  rods.- 

No.  280.1.  At  a load  of  11000  lb.,  deflection  .036  in., 
tne  first  cracks  appeared,  10  in.  right , 5 in.  right  and  9 in. 
left  of  the  center  of  the  beam.  The  one  10. in.  right  6 in.  long 
others  4 and  3 in.  A crack  6 in.  long  appeared  2 in.  left  of  the 


center  and  one  3 in.  long  at  20000  lb.,  deflection  .0894  a diag- 
onal crack  4 in*  long  appeared  9 in*  from  right  support*  At 
22000  lb.  this  crack  had  a length  of  9 in,  other  cracks  not 
lengthning  at  23800  lb.  the  beam  failed  suddenly  by  diagonal 
tension  and  bond  at  crack  9 in.  rrom  right  support.  The  position 
and  movements  of  defle ctometers  may  be  seen  on  the  diagram  and 
curves  of  Fig.  17. 

No.  280.2.  At  1200U  lb.,  deflection  .0475  in.,  the  first 
cracks  appeared,  one  3 in.  long  4 in.  left  of  center  one  4 in.  long 
14  in.  right  of  center*  At  14000  lb.,  deflection  .0548  in.,  crack 
5 in.  long  3 in.  left  of  left  lord  and  a crack  5 in.  long  9 in. 
right  of  right  load.  At  16000  lb.  the  last  crack  had  extended 
2 in.  and  another  diagonal  crack  7 in.  long  appe  red  8 in.  from 
right  support.  At  18000  lb.  a diagonal  crack  appeared  y in.  from 
left  support.  At  18800  lb.  the  Deam  failed  suddenly  oy  diagonal 
tension- and  Dona  at  tne  crack  3 in.  from  right  support.  All 


cracks  except  tnat  at  whicn  failure  occured  closed  up.  xne 
concrete  split  along  the  plane  of  tne  reinforcing  bars  from  the 
crack  to  tne  right  end  of  beam. 


■ 


■ 


. 

' 


24. 


Ho..  280.3.  At  12000  lb.,  deflection  .0394  in.,  three 
crocks  appeared,  one  under  right  load  3 in.  long,  one  at  center 

3 in.  long,  one  3 in.  left  of  left  load  2 in.  long.  At  14000  lb. 
three  other  cracks  appeared,  3 in.  right  of  center,  10  in.  left 
of  center  and  a diagonal  crack  5 in.  long,  12  in.  from  left 
support.  At  16000  lb.  diagonal  crack  extended  toward  load  point 

4 in.  At  18C00  lb.  diagonal  crack  had  extended  2 l/2  in.  further. 
At  20000  lb.  center  crack  opened  3 in.  higher.  At  21000  the 
beam  failed  suddenly  by  diagonal  tension  while  the  machine  was 
stopped.  The  concrete  split  along  reinforcement  as  in  beam  280. 2, 
see  diagram  Fig. 19. 

Beams  reinforced  with  Gabriel  Units. - 

Ho.  281.1.  At  16000  lb.  deflection  .0518  in.,  first 
cracks  appear;  one  3 in.  long  under  right  load,  one  4 in.  long 

5 in.  left  of  left  load,  and  one  2 in.  long  7 in.  right  of  right 
load.  At  17000  lb.  two  cracks  3 l/2  long  appear  near  center  of 
the  beam.  Progress  of  the  cracks  may  readily  be  traced  on  the 
diagrams.  At  18000  lb.,  deflection  .061  in.,  the  first  diagonal 
crack  appears.  At  36400  lb.  the  load  fell  off  rapidly  to  356CC 
then  rising  slowly  to  an  ultimate  load  of  40000  lb.  cracks  near 
the  center  began  opening  at  36000  lb.  and  were  l/8  in.  wide  when 
the  load  reached  40000.  Compression  in  the  concrete  at  this  load 
was  confined  to  a region  3 in.  deep  from  the  top  of  the  beam  and 
failure  occurred  by  crushing  of  upper  portion  due  to  large  stretch 
in  the  steel. 

Ho.  281.2.  The  first  crack  appesred  at  10000  lb., 
deflection  .0306  in.,  near  the  center  of  the  beam.  At  14000  lb. 
this  crack  was  5 l/2  in.  long,  at  27000  lb.  a diagonal  crack  8 in. 


I 


25. 


long  hsd  appeared  10  In.  from  right  support.  At  55000  lh.  the 
deflection  was  .205  in.  After  passing  this  load  the  heain  deflect- 
ed beyond  the  limit  of  the  deflectometer  and  the  load  rose  very 
slowly.  Failure  occurred  in  the  same  manner  as  beam  281.1.  The 
diagonal  crack  on  the  right  end  had  reached  within  2 in.  of  the 
top  of  the  beam  at  a point  6 in.  right  of  the  right  load.  The 
portion  of  the  web  subjected  to  tension  shov/ed  rapid  deformation 
after  the  load  passed  26000  lb. 

No.  281.3.  At  10000  lb.,  deflection  .0248  in.  the 
first  crack  appeared  at  the  center  of  team.  At  12000  lb.  crack 
was  3 in.  long;  three  other  cracks  appear,  2 in.  left  of  right 
load,  5 in.  right  of  center  and  1 in.  right  of  left  load.  At 
16000  lb.  deflection  .0528  in. , a diagonal  crack  6 in.  long  ap- 
peared 9 in.  from  left  support.  At  18000  lb.  a similar  crsck 
appeared  9 in.  from  right  support.  Frogress  of  cracks  may  be 
traced  on  diagram  Fig.  21.  • At  35000  lb.  crsck5in.left  of  center 

of  beam  forked  within  3 in.  of  the  top  of  the  beam;  cracks  near 

en> 

center  opening  rapidly,  diagonal  cracks  lengthing  fsst.  At 

n 

36720  concrete  failed  in  compression  due  to  stretch  in  steel. 

The  deflection  of  the  beam  at  the  maximum  load  was  about  .5  in. 
Tension  deformations  of  the  web  were  very  similar  to  beam  251.2. 

No.  281.5  At  10000  lb.,  deflection  .037  in., first  cracks, 
onea  diagonal  crack  9 in.  left  of  left  load  the  other  vertical 
2 in.  left  of  center  of  beam  both  4 in.  long.  At  12000  a crack 
4 1/2  in.  long  6 in.  right  of  center  appears.  At  24000  lb. 
diagonal  crack  9 in.  from  left  load  within  5 in.  of  top  of  beam. 

At  34000  lb.  diagonal  crack  within  2 in.  of  top  of  beam  and  under 
left  load.  At  35000  lb.  the  crack  6 in, right  of  center  8 in. 


26. 


. rn 

long.  At  36000  lb.,  deflection  .233  in.,  linit  of  deflectometer 
soon  passed,  deflections  increased  rapidly  with  load.  At  40000  lb. 
cracks  in  center  region  of  bean  opening  rapidly.  At  41000  lb. 
failure  of  concrete  in  center  of  beam  a piece  of  concrete  1 l/2-in. 
thick  9 in.  long  snapped  off  of  upper  part  of  beam.  The  deforma- 
tions of  the  web  of  this  beam  were  greater  than  the  deformations 
of  beams  281.2,  281.2  and  281.3  (see  diagram  and  curves). 

ITo.  281.6.  First  crack  appeared  under  right  load  at 
10000  lb.  At  12000  lb.,  deflection  .0475  in.,  crack  4 in.  long 
2 in.  right  of  center,  crack  2 l/2  in.  long  6 in.  left  of  center. 

At  14000  lb.,  deflection  .0634  in.,  diagonal  crack  4 in.  long  6 
in.  left  of  left  load  and  a diagonal  crack  6 in.  long  at  6 in. 
from  left  load.  At  34000  lb.  the  cracks  in  the  center  region  of 
beam  were  about  6 in.  long  and  the  first  diagonal  crack  had  reach- 
ed a po.nt  within  2 in.  of  the  top  of  the  beam  under  the  left  load 
deflection  about  .25  in.  At  37850  lb.  beam  failed  by  diagonal 
tension.  The  long  diagonal  crack  forming  suddenly,  see  diagram 
Fig.  23.  Hooks  on  lower  rods  bend  out  snapping  off  concrete  at 
end  of  beam.  Truss  rod  split  beam  vertically  in  center  at  left 
end  full  depth  of  beam  and  18  inches  along  the  top.  Web  deforma- 
tions especially  noteworthy.  Vertical  cracks  near  the  center  of 
the  beam  closed  at  release  of  load. 

, ITo.  281.7.  At  12000  lb.,  deflect  ion.  039  in.,  two  cracks 
noted;  one  4 l/2  in.  long  7 in.  right  of  center  and  one  3 in.  long 
at  center  of  beam..  At  180CC  lb.,  deflection  .0688  in.,  first  diag- 
onal cracks  noted.  At  22000  lb.  a diagonal  crack  on  right  end 
opens  from  center  height  to  within  2 in.  of  the  bottom  of  beam. 

At.  24000  the  last  diagonal  crack  ‘opens  to  bottom  of  beam  and  a 

diagonal  crack  10  in.  long,  6 in.  from  left  support  extends  in  a 


_ 


Z7 


straight  line  at  an  angle  of  45°  to  the  horizontal.  At  32000  lt>. 
the  lest  crack  within  2 l/2  in.  of  top  of  bean  end  inclined  toward 
loed  point.  At  39000  lb.  deflection  of  beam  .51  in.  At  40CCC  lb. 
diagonal  crack  on  right  end  of  beam  extends  to  within  two  inches 
of  top  of  team  3 in.  right  of  load,  diagonal  crack  on  left  extends 
to  within  1 l/4  in.  of  top  of  team  2 in.  left  of  load.  Beam  fail- 
ed by  compression  in  concrete  due  to  stretch  of  steel  in  center 
third  of  beam. 

Beams  reinforced  with  Monolith  Bars. 

Ho.  282.1.  At  14000  lb.,  deflection,  .0428  in.,  first 
crack  appeared  under  left  load.  The  second  and  third  cracks  ap- 
peared at  a load  of  16000  lb.,  one  being  a diagonal  crack  6 in. 
right  of  the  right  load*  At  £2000  lb.  the  first  crack  forked  at 
the  mid  height  of  the  beam;  crack  Ho.  6, which  had  appeared  at 
18000  lb.  load, also  forked  in  the  same  manner*  At  29100  lb. 
initial  failure  occurred  by  tension  in  the  steel  near  the  center 
of  the  beams,  apparently  passing  the  yield  point*  At  32000  lb. 
the  concrete  failed  by  crushing  at  the  top  of  the  beam  as  shown  in 
the  photograph  Pig. 5.  Extensometers  A,  B,  and  C showed  pecu- 
liar deformations,  due  probably  to  the  forking  of  the  cracks  with- 
in the  middle  third  of  the  beam,  Pig  25. 

Ho.  282.2.  At  10000  lb.,  deflection  .0348  in.,  the 
first  cracks  we re  noted^one  9 in.  to  the  right  of  the  center  ex- 
tended 5 in.  high  and  somewhat  inclined,  one  8 in.  left  of  the 
center  4 in.  high  and  one  14  in.  left  of  the  center  extending  3 l/2 
in.  high.  At  1600C  lb.  the  two  principal  diagonal  cracks  appeared. 
At  26000  lb.  the  diagonal  crack  on  the  ri  ht  had  extended  to  with- 
in 3 in.  of  the  load  point.  At  30000  lb.  the  cracks  near  the 


28. 

center  of  the  beam  were  opening  rapidly  and  one  forked  like  those 
of  beam  282.1.  These  cracks  opened  to  within  2 in.  of  the  top  of 
the  beam  and  at  32000  lb.  crushed  the  concrete  as  shown  in  Fig.  5. 
One  of  the  pecularities  of  this  beam  was  the  compression  shown 
in  the  second  stirrup  on  the  left  by  extensometei  A.  Fig.  26. 

No.  282.3.  The  first  cracks  developed  in  this  beam  at  3 
and  11  in.  left  of  the  center  at  a load  of  9000  lb. ; the  one  near- 
est the  center  showing  only  above  the  reinforcing  bar  and  not  to 
the  bottom  of  the  beams.  At  10000  lb.  a diagonal  crack  was  noted 
above  the  first  stirrup  on  the  right.  At  18000  lb.  a diagonal 
crack  from  junction  of  second  stirrup  on  the  right  developed.  This 
crack  never  crossed  the  first  stirrup.  At  22000  and  26000  lb. 
cracks  developed  at  the  junction  of  the-  third  stirrups  right  and 
left.  At  30000  lb.  the  crack  near  the  center  opening  rapidly, 
deflection  .25  in.  at  329CC  lb.  concrete  began  to  crush  at  top, 
load  remained  constant  till  the  deflection  reached  1.0  in.  The 
load  then  rose  slowly,  reaching  the  maximum  at  33850  lb .,  deflection 
1.2  in.  At  32500  lb .,  deflection  14  in.,  a large  piece  of  concrete 
split  up  between  load  points  as  shown  in  the  photograph.  Fig.  5. 
a large  deformation  occurred  in  the  stirrups  at  the  right  end  of  the 
beam. 

Beams  reinforced  with  American  System  Unit  Frames. 

No.  283.1.  This  beam  was  not  whitewashed  and  hence  it  is 
thought  that  the  cracks  could  not  be  seen  in  their  early  stages. 

At  20000  lb.,  deflection  .0702  in.,  two  cracks  were  noted,  one  a 
diagonal  crack  12  in.  from  right  support.  At  21000  lb.  a diagonal 
crack  appeared  12  in.  from  the  loft  support.  At  22000  lb.  a crack 
3 in.  high  appeared  at  the  center  of  the  beam.  At  33000  lb.  the 


29. 


diagonal  crack  12  in.  from  the  left  support  was  10  in.  long.  At 
56000  lh . the  deflections  became  more  rapid;  another  diagonal 
crack  formed.  At  50900  lh • the  beam  failed  suddenly  by  diagonal 
tension  breaking  the  beam  end  in  several  places  and  slivering  a 
long  piece  off  of  the  top  of  the  beam. 

Ho.  285.2.  At  10000  lh.,  deflection  .0558  in.,  four 
cracks  were  noted,  one  12  in.  from  right  support  4 in.  high 
vertically  along  second  stirrup,  one  4 in.  high  under  the  right 
load  point,  one  4 in.  high  2 in.  right  of  the  left  load  point, 
one  5 in.  high  vertically  along  second  stirrup  on  left  end.  First 
cracks  entirely  symmetrical.  At  14000  lh . the  cracks  at  second 
stirrups  inclined  toward  the  load  points  at  the  junction  of  the 
vertical  stirrup  with  the  inclined  rod.  At  24000  lh.  the  right 
and  left  inclined  cracks  respectively,  had  reached  within  5 and 
4 l/2  inches  of  the  top  of  the  beam.  At  26000  lh . the  beam  fail- 
ed suddenly  by  diagonal  tension  at  the  left  end  of  the  beam  very 
much  in  the  same  manner  as  beam  285.1.  It  i3  noteworthy  that  the 
deformations  on  the  right  and  left  ends  of  the  beam  were  so  nearly 
equal  throughout  the  test  as  shown  by  the  curves  of  Fig.  28. 

Ho.  285.5.  This  beam  had  a depth  of  12  in.  instead  of 
11  in.,  the  depth  of  other  beams  of  this  class.  At  12000  lh., 
deflection  .0516  in.  a crack  5 in.  long  appeared  4 in.  right  of 
the  center.  At  14000  lh . a crack  appeared  under  the  left  load. 

At  20000  lh.  a diagonal  crack  5 in.  long  was  noted  near  the 
second  stirrup  on  the  right.  At  24000  a diagonal  crack  6 in. 
long  occurred  at  tne  third  stirrup  on  the  right  end.  At  54000  lh. 
deflection  .161  in.,  sudden  failure  occurred  by  an  entirely  new 
crack  from  the  right  support  inclining  toward  the  load  point. 


30  . 

The  failure  cracks  are  very  much  like  those  of  beams  283.1  and 
283.2. 

Ho.  283.5.  This  beam  was  not  whitewashed.  At  22000  lb., 
deflection  .086  in.,  two  cracks  each  3 in.  long  appeared  9 inches 
from  the  supports.  At  24000  lb.  three  other  cracks  appeared,  one 
under  each  load  point  and  one  2 in.  right  of  the  center  of  the 
beam.  At  290001b.  cracks  opening  slightly.  At  32000  lb.,  deflec- 
tion .162  in.,  failure  occurred  by  diagonal  tension  at  right 
support . 

Ho.  283.6.  The  first  cracks  were  noted  at  12000  lb.  load. 
There  were  three,  2 to  3 in  high;  one  diagonally  from  bottom  of 
the  first  stirrup  on  the  right,  one  5 in.  left  of  center,  and  one 
vertically  along  the  second  stirrup  on  the  left.  At  22000  lb.  a 
crack  appeared  within  the  web  of  the  beam  near  the  right  support 
but  did  not  reach  to  the  bottom  of  the  beam.  At  24000  lb.  this 
crack  was  8 in.  long.  At  27600  lb.,  deflection  .1625  in.,  the 
beam  failed  suddenly  by  diagonal  tension  at  the  right  support,  a 
second  crack  opened  parallel  to  the  one  which  appeared  at  the  load 
22000  lb.  The  web  deformations  of  this  beam,  while  slight,  show 
very  uniform  curves . 

Ho.  283.7.  At  10000  lb.  2 cracks  appeared  in- this  beam, 
one  5 in.  right  of  the  center  and  one  2 in.  left  of  the  left  load. 
At  14000  lb.  cracks  appeared  vertically  along  the  second  stirrup 
on  the  right  and  the  third  on  the  left  of  the  center.  At  18000 
lb.  a diagonal  crack  8 in.  long  appeared  at  the  fourth  stirrup  on 
right.  At  26000  lb.  a similar  crack  appeared  on  the  left.  At 
30000  lb.  a crack  from  the  left  support  broke  across  to  the  pre- 
vious diagonal  crack.  At  31850  lb.  failure  occurred  by  diagonal 


31. 


tension  at  the  left  end.  The  load-deformation  curves  for  compres- 
sion and  tension  show  nearly  a straight  line  relation  after  passing 
8000  Ih. 

Beams  reinforced  with  C©rrbar  Unit  Frames. 

Ho.  284.1.  At  16000  lb.,  deflection  .CUSS  in.,  the  first 
cracks  appeared,  one  12  in.  right  of  the  right  load  point,  one 
under  the  right  load  point  and  one  5 in.  right  of  the  center. 
Cracks  appeared  at  different  intervals  of  loading  until  16  al- 
together were  noted,  half  of  these  were  within  the  middle  third 
of  the  beam.  At  40000  lb.  a diagonal  crack  formed  at  the  right 
support,  at  42000  lb.  a similar  crack  at  the  left  support.  At 
49000  lb.  the  deflect ometer  reached  its  limit  at  .27  in.  At 
52750  lb.  the  beam  failed  by  compression  in  the  concrete  due  to 
the  rapid  stretching  of  the  steel.  The  web  deformations  as  re- 
corded by  the  extensometers  show  a fairly  uniform  rate  of  defor- 
mation. 

ITo.  284.2.  At  11000  lb.,  deflection  .0405  in.,  the  first 
crack  appeared  under  the  left  load.  At  16000  lb.  three  diagonal 
cracks  appeared,  two  on  the  right  and  one  on  the  left.  At  24000 
lb.,  deflection  2 in.,  a diagonal  crack  8 in.  long  appeared  6 in. 
from  the  right  support.  At  48000  lb.  the  diagonal  crack  on  the 
right  had  reached  a point  1 ]/E  inches  from  the  top  of  the  beam. 

At  49300  lb.  the  concrete  crushed  between  the  load  points.  After 
the  release  of  the  load  the  large  crack  near  the  center  of  the 
beam  closed  almost  completely.  It  is  thought  that  the  stress  of 
the  steel  did  not  exceed  the  elastic  limit. 

Ho.  284.3.  At  12000  lb.,  deflection  .0430,  the  first 
crack  appeared  5 in.  left  of  the  center  of  the  beam.  At  14000 


32. 


lb.  the  first  diagonal  crack  appeared  6 in.  right  of  the  right 
load,  also  a crack  under  the  left  load  point.  At  30000  lb.  a 
large  diagonal  crack  appeared  near  the  right  support*  At  44000 
lb.  a diagonal  crack  8 in.  long  opened  6 in.  from  the  left  support. 
At  47500  lb.  the  beam  failed  suddenly  by  diagonal  tension  at  the 
left  support.  A long  sliver  of  concrete  broke  from  the  top  of 
the  beam. 


crack  appeared  near  the  center  of  the  beam.  At  14000  lb.  the 
first  diagonal  crack  appeared  12  in.  from  the  right  support.  At 
22000  lb.  a diagonal  crack  6 in.  from  the  right  support.  At  36000 
lb.  the  crack  near  the  right  support  opening;  cracks  at  center 

V 

opening  but  not  lengthening.  At  48000  lb.  the  diagonal  crack  near 
right  support  opening  rapidly.  At  54400  lb.  the  beam  failed  by 
crushing  in  concrete  after  the  stress  of  the  steel  had  passed  the 
yield  point.  The  web  deformations  of  this  beam  were  very  regular. 


left  of  the  center,  at  the  junction  of  the  first  stirrup.  At 
14000  lb.  one  crack  appeared  under  the  left  load  point  and  one 
at  the  center  of  the  beam.  At  24000  lb*  diagonal  cracks  opened 
6 in.  from  each  support.  At  50000  lb.,  deflection  .33  in.,  the 
beam  failed  by  crushing  of  concrete  and  stretch  of  the  steel. 
Steel  took  some  set*  The  web  deformations  were  slight  until  the 
load  had  passed  16000  lb. 

ITo.  284.7.  At  120°0  lb.,  deflection  .055  in.,  three 
cracks  appeared,  one  3 in.  right  of  the  right  load  point,  one 
under  the  left  lord  point  and  one  12  in.  left  of  the  left  load 


Ho.  284.5.  At  12000  lb.,  deflection  .037  in.,  the  first 


Ho.  284.6.  At  10000  lb.  the  first  crack  appeared  6 in 


. 


' 


* 


' 


. 


« 


33. 


point.  At  24000  lb.  a diagonal  crack  4 in.  long  4 in.  from  the 
right  support.  At  32000  lb.  two  cracks  near  the  center  were 
7 1/2  in.  high,  the  diagonal  crack  on  the  right  end  opening  rap- 
idly. At  43000  lb.  a diagonal  crack  9 in.  long  formed  at  the 
left  support.  At  50950  lb.  the  beam  failed  by  stretch  of  the 
steel  and  subsequent  crushing  of  the  concrete.  The  web  defor- 
mations in  this  beam  were  the  most  irrqjilar  of  any  of  the  beams 
reinforced  with  the  Corrbar  Units. 

Beams  reinforced  with  the  General  Fireproofing  Company's  Units. 

No  285.1.  At  10000  lb.,  deflection  .0310  in.,  a vertical 
crack  was  noted  at  the  center  of  the  beam.  At  14000  lb.  three 
cracks  were  noted  at  the  junction  of  stirrups  with  the  main  rod. 

At  18000  lb.  cracks  formed  at  the  third  stirrups  on  each  end.  At 
26800  lb.  the  stirrup  clips  began  to  slip  along  the  main  rod. 

The  maximum  load  reached  was  27100  lb.  The  deformations  of  the 
web  were  very  small  before  the  slip  of  the  stirrups  occurred.  It 
should  be  noted  here  that  a second  stirrup  on  each  bar  was  broken 
in  making  the  beam  one  on  one  end,  the  other  on  the  other;  and 
that  one  bar  had  the  second  clips  on  each  end  broken.  This  ac- 
counts for  much  of  the  weakness  of  the  beam. 

Ho.  285.2.  At  12000  lb.,  deflection  .0366  a crack  3 in. 

, in  high  was  noted  1 in.  left  of  the  center.  At  18000  lb.  a crack 
was  noted  at  the  junction  of  the  second  stirrups  on  each  end.  At 
34000  lb.  all  cracks  very  small.  At  36000  lb.  the  cracks  at  the 
junction  of  the  first  and  second  stirrups  opening.  At  36600  lb. 

deflection  .17  in.,  the  beam  failed  by  slip  of  the  stirrup  clips 
along  main  rod  and  by  bond  of  the  concrete.  This  beam,  also  had 

Lsome  broken  stirrups  on  one  of  the  units,  the  first  on  one  end 


■ 


34. 


and  the  fourth  on  the  other. 

Ho.  285.3.  At  10000  lb.,  deflection  .0225  in.,  the  first 
crack  appeared  at  the  center  of  the  beam.  At  16000  lb.  a crack 
appeared  at  the  junction  of  the  second  stirrup  on  the  left.  At 
22000  lb.,  cracks  appeared  at  the  junction  of  the  second  and  third 
stirrups  on  the  right.  At  34000  lb.  the  machine  was  allowed  to 
stand  several  minutes  the  load  dropping  off  to  30800  lb.  The  diag- 
onal cracks  at  this  load  were  about  8 3 J 2,  in.  long.  At  59600  lb. 
the  beam  failed  by  failure  of  bond  and  slip  of  stirrup  clips  along 
the  main  rods  on  the  left  end.  The  load  dropped  off  very  rapidly. 
The  web  deformation  diagrams  are  not  noteworthy. 

Ho.  285.5.  The  first  cracks  were  noted  at  a load  of 
14000  lb.  opening  from  the  junction  of  the  second  stirrups  on  each 
end.  At  36000  lb.  the  cracks  we re  all  very  small.  At  40000  lb., 
deflections  increased  very  rapidly  with  an  increase  of  the  load 
Movement  of  main  rod  in  concrete  noticeable  at  the  end.  The  max- 
imum load  was  40400  lb.  Stirrups  slipping  along  the  main  rods 
continued  the  deflection  of  the  beam  until  the  load  dropped  to 
57000  lb.  A large  piece  of  concrete  broke  from  the  bottom  of  the 
beam  and  was  pulled  off.  See  Fig.  9. 

Ho.  285.6.  The  first  crack  occurred  10  in. left  of  the 
center  at  a load  of  12000  lb.,  deflection  .0304  in.  At  22000  lb. 
two  diagonal  cracks  were  noted,  one  4 in.  right  o*0  the  right  load 
point  the  other  8 in.  left  of  the  left  load  point.  At  40000  lb. 
snapping  sounds  within  the  beam  probably  due  to  failure  of  stir- 
rups. The  load  reached  a maximum  of  41900  lb.  and  gradually  fell 
off  as  deflection  increased.  Failure  resulted  from  the  slipping 
of  stirrups  along  the  main  rods  and  failure  of  bond  on  the  right 


35. 


end.  The  weh  deformations  in  the  left  end  of  the  beam  were  very 
slight,  especially  so  in  elongation  of  stirrups,  compression  de- 
format  ions  were  more  marked. 

Ho.  285. V.  At  13000  lb.  the  first  crack  appeared  at  2 
in.  right  of  the  center.  At  18000  lb.  a diagonal  crack  3 in.  long 
was  noted  at  the  junction  of  the  first  stirrup  on  the  right.  At 
20000  lb.  a diagonal  crack  4 in.  long  was  noted  at  the  junction 
of  the. third  stirrup  on  the  left.  At  32000  lb.  the  stirrups  on 
the  right  end  of  the  beam  began  slipping.  At  34450  lb.  the  max- 
imum load  was  reached.  Stirrups  slipping  in  rapid  succession. 
Deflection  of  beam  was  continued  until  the  load  fell  off  to  28000 
lb»  A#  30000  lb.  a stirrup  or  clip  bro#e . The  cirve  of  compression 
in  the  concrete  is  especiallj'-  noteworthy,  ?ig.  43. 


1 


36  . 

CONCLUSIONS. 

From  these  tests  it  is  seen  that  the  beams  reinforced 
with  plain  rods  only  deflect  no  more  than  beams  with  web  reinforce- 
ment for  stresses  up  to  the  safe  working  stress  of  concrete.  When 
the  shearing  stress  of  a beam  is  large  as  compared  with  the  flexure 
stress,  ample  web  reinforcement  should  be  used  to  insure  against 
the  sudden  failure  by  diagonal  tension  which  is  characteristic  of 
short  beams  reinforced  with  plain  rods  only.  For  beams  made  of  the 
quality  of  concrete  used  in  these  tests  the  average  unit  shearing 
stress,  in  order  that  the  beams  may  have  the  proper  factor  of 
safety,  should  not  exceed  40  lb.  per  sq.  in.  Beams  with  dependable 
web  reinforcement  may  have  shearing  stresses  somewhat  higher,  but  not 
in  any  case,  however,  to  exceed  75  lb.  per  sq . in.,  as  greater  stress 
would  likely  cause  diagonal  cracks  to  open. 

Beams  reinforced  with  Gabriel  Units  were  effective  in 
carrying  loads,  but  under  the  conditions  of  the  tests  they  showed 
more  deformation  in  the  region  of  the  web  than 'is  desira.ble  . A con— 
siderable  part  of  this  deformation  could  probably  be  prevented  by 
inclining  the  tops  of  the  stirrup  toward  the  ends  of  the  beams. 

The  deflection  and  strength  of  beams  No.  281.5  to  281.7,  show 
that  the  trussed  rod  used  with  the  Gabriel  Units  is  more  effective 
in  the  last  stages  of  deformation  than  in  the  early  stages.  The 
deflection  curve  for  these  beams  shows  an  upward  turn  at  a load 
of  24000  lb.,  indicating  that  the  inclined  rod  is  most  effective 
after  this  load.  The  hooks  on  the  ends  of  reinforcing  rods  tend  to 
prolong  the  life  of  the  beam. 

The  beam  reinforced  with  Monolith  Units  show  that  mild 


37. 


steel  does  not  make  as  effective  reinforcing  as  does  high  carbon 
steel.  The  method  of  anchoring  the  stirrur  to  the  main  rod  of 
these  units  is  a most  effective  one. 

Failures  of  beams  reinforced  with  American  System  Unit 
Frames  were  in  all  cases  by  diagonal  tension  and  in  all  cases  but 
one  very  sudden,  indicating  that  vertical  stirrups  do  not  insure 
a satisfactory  distribution  of  the  stress.  The  fabricated  frame 
showed  only  slight  superiority  in  strength  and  stiffness  over  the 
loose  rod  frame.  The  increased  strength  will  not  justify  the  use 
of  the  extra  metal  and  labor  required  in  the  fabrication  of  this 
type  of  reinforcement. 

The  most  effective  reinforcement  of  the  several  types 
tested  was  the  Corrbar  Unit,  manufactured  by  the  Corrugated  Bar 
Company  of  St.  Louis.  In  nearly  every  respect  this  system  showed 
superiority  over  others.  For  such  conditions  of  loading  as  were 
obtained  in  these  tests  this  reinforcement  was  well  proportioned. 
7/ire,  as  used  for  the  web  system  of  beams  II o . 284.1  to  284.3,  v/ill 
prove  sufficient  for  beams  subjected  to  ordinary  conditions  of 
loading.  The  effectiveness  of  high  carbon  steel  as  a reinforcing 
material  is  shown  by  a direct  comparison  of  the  beams  reinforced 
with  these  units,  with  those  reinforced  with  Monolith  Units,  the 
percentage  of  horizontal  metal  in  each  case  being  1.6.  The  maxi- 
mum loads  supported  by  the  latter  averaged  only  65  per  cent  of 
those  supported  by  the  former. 

The  use  of  high  carbon  steel  does  not  guarantee  economy 
unless  care  is  used  in  the  design,  fabrication  and  handling  of  the 
reinforcement.  II o better  illustration  of  this  can  be  given  than 
the  results  of  the  use  of  the  General  Fireproofing  Company's  Units. 


, 


. 


38. 


two— third 8 

In  no  case  was  the  horizontal  steel  stressed  much  beyonu  of 

the  elastic  limit  and  in  most  cases  much  less  than  this.  The 
weak  point  of  this  system  of  reinforcing  is,  the  connection  of 
the  stirrups  to  the  main  rods.  These  connections  allow  the  stir- 
rups to  slip  much  before  the  elastic  limit  of  the  stirrup  steel 
is  reached,  causing  premature  failure  of  the  beam  and  giving  poor 
economy  of  reinforcing  material.  Another  feature  of  this  system 
of  reinforcing,  which  makes  its  economy  still  more  doubtful,  is 
the  liability  of  breakage  of  the  stirrups  and  stirrup  clips  in  the 
handling  preparatory  to  placing  in  the  forms.  With  careful  hand- 
ling in  the  laboratory  seven  breaks  of  stirrups  and  clips  were 
noted  in  the  twelve  units,  when  they  were  ready  to  be  placed  in 
the  forms.  If  the  connections  to  the  main  rods  were  made  to  de- 
velop the  strength  of  the  stirrups  and  the  liability  of  breakage 
overcome  in  some  manner,  this  system  of  reinforcement  would  prob- 
ably be  as  good  as  any  system  in  which  the  stirrups  are  inclined, 
as  the  spacing  of  stirrups  can  be  regulated  to  suit  the  case  in 
hand  and  the  fabrication  quickly  and  cheaply  done. 

In  reinforced  concrete  beams  the  lines  of  principal 
% 

stress  are  very  much  like  those  in  a beam  of  homogeneous  material 
until  cracks  form.  In  beams  having  inclined  stirrups  the  lines 
of  principal  stress  in  the  lower  half  of  the  beam,  after  cra.cks 
are  well  developed,  seem  to  follow  lines  inter  mediate  between 
those  of  the  truss  and  the  beam  of  homogeneous  material.  (See 
Concrete-Steel  Construction  by  Prof.  E.  Korsch,  trans.  by  E.  P. 
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PIG. 31.  LOAD  - DEFORMATION  DIAGRAM  PGR  BEAM  H0.2M3.7 
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PIG. 44.  DIAGRAM  OP  DEFORMATIONS  AND  POSITION  OP  NEUTRAL  AXIS. 

BEAM  NO.  080.3 

Scale  of  Deformations  1=.0005.  Loads  in  0000  lb . Increments . 

Ultimate  Load  33850  lb. 


PIG. 45.  DIAGRAM  CF  DEFORMATIONS  AND  POSITION  OP  NEUTRAL  'XIS. 

BEAM  110.283.7 

Goal-?  of  Deformations  1=.0005.  Loads  in  2000  lb.  Increments. 

Ultimate  Lend  31850  lb. 


82. 


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FIG. 46.  DIAGRAM  OF  DEFORMATIONS  AND  POSITION  OF  NEUTRAL  AXIS. 

BEAM  NO.  08 <1.3 

Scale  of  Deformations  1~.0005.  Loadc  in  °000  lb.  Increments. 


Ultimate  Load  47500  ib. 


83. 


OF  NEUTRAL  AX 


03 ITT on 


BEAM  NO.  284 


lb.  Increments 


of  De f ornations  ls=.0005.  Loads  in  2000 


Ultimate  Load 


84 


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PIG. 46.  DIAGRAM  0?  DEFORMATIONS  AIID  POSITION  OF  NEUTRAL  AXI; 

BEAM  HO. 285. 7 

Scale  of  Deformations  1=.0005  Loads  in  2Q00  lb . Increments . 

Ultimate  Load  lb. 


